Semiconductor devices, such as switching devices or diodes, are used in circuits, such as switching power supplies or inverters. The semiconductor devices require a high breakdown voltage and low on resistance. A trade-off relationship which is determined by a semiconductor material is established between the breakdown voltage and the on resistance.
With the progress of technical development, the on resistance of the semiconductor device has been reduced to a value close to the lower limit of the on resistance of silicon which is a representative semiconductor material. It is necessary to change the semiconductor material in order to further increase the breakdown voltage or to further reduce the on resistance. A GaN-based semiconductor, such as GaN or AlGaN, or a wide bandgap semiconductor, such as silicon carbide (SiC), is used as the semiconductor material of the switching device to improve the trade-off relationship determined by the semiconductor material and to achieve a high breakdown voltage or low on resistance.
In a metal insulator semiconductor field effect transistor (MISFET) using the GaN-based semiconductor, there is a concern that a threshold voltage will vary due to the trapping of charge.